Conventional libraries, such as peptide libraries which have been widely used in the field of combinatorial chemistry or new drug development, generally consists of amino acids whose chemical structures are already known. Conventional libraries have largely depended on the method of manufacturing various combinations of compounds by repeatedly combining structurally diverse compounds.
However, conventional libraries have limits in diversity since compound components constituting the library are constructed from chemical synthesis.
In addition, conventional libraries have been extensively explored by many researchers in the field of new drug development.
On the contrary, compounds in the natural products containing herbal drugs are great in numbers and frequently contain compounds, such as optical isomer, that are difficult to synthesize using current organic synthesis technology. Compounds in the natural products possess much more variety in property and chemical structure than the compounds synthesized by organic synthesis.
Therefore, considerable efforts have been devoted by many researchers to search and discover useful substances from natural products. But these researches have generally been directed to obtaining useful compounds using the general method of isolation and purification, i.e. isolation and purification according to the solubility, adsorbency and size.
Conventional methods generally employed in searching biologically active materials are as follows: First, water-soluble or oil-soluble materials are isolated according to their physical or chemical properties. And pharmaceutical or biological activities are assayed on the crude extract obtained using adsorption chromatography, thin layer chromatography, gel filtration chromatography and/or ion exchange chromatography. Then, additional extraction and isolation using said chromatographies is conducted on the fraction of crude extract showing specific activity, and finally the biologically active compounds are isolated and purified.
But in the pharmaceutical or biological assays of unpurified crude extracts, there can be errors due to the additive effect which often shows more excellent activity than that of the single compound.
In addition, said methods of searching biologically active materials have defect in that since the methods use extraction, isolation and purification several times on the general compounds, the method cannot find biologically active materials which exist in small amounts in extract.